Grid-cathode assembly for cathode ray tubes



March 20, 1962 T. P. WARNE, JR

GRID-CATHODE ASSEMBLY FOR CATHODE RAY TUBES Filed June 5, 1958 IN VENTOR.

THums P WARNEJR.

United States Patent Ofiice 3,026,438 Patented Mar. 20, 1962 3,026,438GRID-CATHODE ASSEIVLBLY FOR CATHODE RAY TUBES Thomas P. Warne, Jr.,Trout Run, Pa., assignor to Radio Corporation of America, a corporationof Delaware Filed June 5, 1958, Ser. No. 740,082

6 Claims. (Cl. 31382) This invention relates to cathode ray tubes, andin particular to a novel structure for controlling electrode spacing anda novel method of assembly of electrodes.

The exact spacing and alignment of a grid electrode aperture withrelation to an emitting cathode electrode face is very important becauseit determines the efiective control of the grid. The grid aperturealignment and spacing from the cathode emitting face must be accuratebecause it forms part of the first electron lens system by which thebeam is formed and focused. Since it is necessary to have precision inthe spacing and alignment of the cathode and grid, and becauseuniformity of the close spacing of these two electrodes in each tube isrequired in mass production of tubes of the same type, the mechanicaldesign of a grid-cathode unit of an electron gun represents one of theimportant problems in gun design.

The construction of a grid-cathode structure of a conventional type ofelectron gun has involved the difiicult process of assembling many smallparts in proper relationship. The process also involves fixing severalsubassemblies in predetermined spaced relationships involving criticaldistances subject to small tolerances. The distances between parts aregenerally measured by a micrometer dial ga e and spacing adjustments aremade by inserting spacers of various thickness. This method is tediousand time-consuming.

Furthermore, in a conventional electron gun assembly, the heating of thecathode sometimes causes the cathode emitting surface to move closer tothe grid aperture. This change in grid-cathode spacing results fi'om theexpansion of the cathode cylinder when the heater is turned on. Warpingof the grid cylinder due to changes in pressure or temperature may alsoafiect the alignment and spacing of the grid-cathode.

An object of this invention is to simplify the spacing adjustmentbetween electrodes of a cathode ray tube.

Another object of this invention is to provide an improved structure foraccurate control of the spacing from cathode to grid.

Another object is to provide a grid-cathode assembly which is stableunder varying operating conditions.

According to this invention electrodes have co-operating means onadjacent surfaces to provide a spiral action with respect to each otherupon relative rotation. Spacing of the electrodes is controlled byrotation of one electrode with respect to another electrode.

According to one embodiment of the invention, which is described indetail in the following specification, a grid cathode assembly includesco-operating means which consist of bosses co-operating with ramps.During assembly of the electron gun the bosses and ramps are engaged anda rotation of the cathode with respect to the grid provides spacingadjustment.

The invention is more fully described in the following detaileddescription when read with the drawing in which:

FIG. 1 is an elevational view partially in section showing thegrid-cathode assembly employing the metallic spacer cylinder;

FIG. 2 is a section taken along the line 22 of FIG. 1 showing one formof the bosses, according to the invention;

FIG. 3 is a perspective view of the metallic spacer cylinder showing theramps;

FIG. 4 is a vertical section showing the grid-cathode assembly employingthe ceramic disk and the retainer; and

FIG. 5 is a perspective view of the ceramic disk in corporating theramps.

The same reference characters are used to denote similar elementsthroughout the drawing.

FIG. 1 of the drawing illustrates an embodiment of the invention inwhich a grid-cathode assembly comprises a metallic grid cylinder 1, ametallic spacer cylinder 3, a ceramic disk 5 and a cathode 7. The spacercylinder 3 and the ceramic disk 5 serve as support structure forsupporting the cathode 7 relative to the grid cylinder 1. The metallicgrid cylinder 1 has a closed end 9 with a relatively small circularaperture 11 centrally located therein. Three elongated bosses 13radially positioned 120 apart are formed in the grid endwall 9. Theelongated bosses 13 are clearly shown in FIG. 2 of the drawing.

The metallic spacer cylinder 3 is an integral structure having a lowercylinder portion 15, and a smaller diameter tubular portion 17 coaxiallypositioned and connected by a shoulder or annular section 19. The lowerportion 15 fits closely into the grid cylinder 1 to allow rotational andlongitudinal motion of the metallic spacer 3 against the grid cylinderWall. The lower portion 15, which is open-ended, has a pair of spacedslots 21 in the wall adjacent the open end. The smaller tubular portion17 has a flanged end 23 on which three gradient sections or ramps 25 areformed.

Each of the ramps 25, illustrated in FIG. 3, delineates a 120 arc of thegenerally annular pattern formed by the flange 23. Each ramp 25 slopesin the same direction along its are at the same angle. Ramps which slope.030 inch in of are have been found to be satisfactory. The flanged end23 is provided with a large aperture 27 through which the cathode 7 maybe projected.

The cathode 7 includes a conventional hollow metallic cylinder 29,closed at one end by a cap portion 31. The outer surface of cap portion31 is coated with an emitting layer 33 of thermionic emitting material,such as a mixture of strontium and barium oxides. This material is wellknown and is recognized as that which easily emits electrons, whenheated to high temperatures. Mounted within the cathode cylinder 29 is aheater filament 35 which is coated with a layer of insulating material.The filament 35 is twisted in a coil formation to provide aunidirectional field when filament 35 is heated with alternatingcurrent. The cathode cylinder 29 is supported within a central aperture39 of the ceramic support disk 5 by peripheral beads 41 pressed out ofthe wall of the cathode cylinder 29 into contact with opposite surfacesof the ceramic disk 5.

During assembly of the grid-cathode unit, the cathode cylinder 29 andattached ceramic disk 5 are inserted into the grid cylinder 1 so thatthe disk 5 rests against the shoulder or annular section 19 of thespacer 3. The cathode 29 is so positioned within the ceramic disk 5 sothat the cathode emitting layer 33 projects from the relatively largeaperture 27 of the spacer. A portion of the wall of the spacer 3adjacent and below the inserted ceramic disk 5 is then crimped torigidly fix the ceramic disk 5 within the spacer cylinder 3 against theshoulder or annular section 19. When so fixed, the cathode 7 and themetallic spacer 3 are spaced in insulated relationship.

The metallic spacer cylinder 3 securing the ceramic disk 5 whichsupports the cathode 7 is telescoped into the grid cylinder 1 therebyengaging the ramps 25 of the spacer 3 with the bosses 13 of the grid 1.Projections 42 of a rubber ended mandrel 43 engage the pair of slots 21at the open end of the spacer 15. By rotating the mandrel 43 the spacercylinder 3 rotates relative to the grid end wall 9. Rotation of thespacer cylinder 3 While the ramps 25 and the bosses 13 are engagedallows the spacer cylinder 3 to move along its longitudinal axis andthus varies the spacing from cathode to grid.

The desired spacing between the cathode emitting layer 33 and the gridaperture 11 may be determined by an electric spark method, or an opticalmethod, or any other suitable method. In the optical method, amicroscope 45 is positioned above the grid aperture 11 whereby thespacing from the grid end wall 9 and grid aperture 11 to the cathodeemitting layer 33 may be viewed and measured. The microscope 45 is sofixed that when the layer 33 is viewed in sharp focus, the desiredspacing from cathode to grid has been effected. Alternatively, in theelectric spark method, the cathode 7 and spacer 3 are moved axiallywithin the grid cylinder 1 toward the grid aperture 11 until a point isreached at which a predetermined potential applied between the cathode 7and grid 1 causes an electric spark from the closed end 31 of thecathode to the grid end wall 9.

When the desired spacing is obtained, the cylindrical wall of themetallic grid cylinder 1 and the close-fitting metallic spacer 3 arewelded together. A desired spacing and relationship between the gridaperture 11 and the cathode emitting face 31 is fixed in this manner.

Changes in temperature may cause warpage of the electrodes. Since bothgrid end wall 9 and the spacer flange 2-3 remain in direct contact andrespond to warpage as an integral structure, changes in temperature donot effect their spacing. This construction of the grid-cathode unitaffords a substantially constant spacing and alignment of the gridaperture 11 relative to the cathode emitter.

In another embodiment of the invention, illustrated in FIGS. 4 and 5,the assembly comprises a grid cylinder 47, a cathode 49, a ceramicspacer or disk 51, and a metallic retainer ring 53. The cathode 49 issubstantially the same as cathode 7 shown in the above embodiment.

The ceramic disk 51 has three gradient portions or ramps 55 on onesurface. These ramps are similar in structure to the ramps 25 describedabove, but may be metallize'd to provide a smooth, uniform surface forallowing the bosses 13 of the grid cylinder 47 to slide freely on theramps 55. The other side of the disk 51 has a pair of spaced slots 57which in one form may be two rectilinear grooves 180 apart.

The cathode 49 is positioned within a central aperture 59 of the ceramicdisk 51 and is supported by peripheral beads 61 pressed out of thecathode cylinder wall into contact with opposite surfaces of the ceramicdisk 51. The ceramic disk 51 serves as support structure for supportingthe cathode 49 relative to the grid cylinder 47.

The metallic retainer ring 53 is a metallic annulus which snugly fitsinto the grid cylinder 47, and which may freely be moved against thegrid cylinder wall. On one surface, the retainer ring 53 has a pair ofprotuberances 65 which may be tightly fitted into the slots 57 of theceramic disk 51 to allow a close engagement of the retainer ring 53 andthe disk 51. On the other annular surface of the retainer ring 53, thereare two spaced slots 67 into which a tool, such as a mandrel 43, may beinserted.

in manufacture, the ceramic disk 51 supporting the cathode 49 isinterlocked with the retainer ring '53 by meansof the disk slots 57 andthe corresponding retainer protuberances 65. The cathode 49 and ceramicdisk 51 are inserted into the grid cylinder '47 with the cathode emitter63 facing the grid aperture. The retainer 53 is next inserted into thegrid cylinder 47 so that the protuberances 65 engage the slots 57 of theceramic disk 51. The metallized ramps 55 of the ceramic spacer 51 engageand grid bosses 13. The mandrel 43 is linked with the retainer slots 67and rotated slowly, thus rotating the retainer ring 53 and the attachedstructure which includes the ceramic disk 51 and the cathode 49. Thesame methods of measuring the grid to cathode spacing, as describedabove, may be employed. The rotation of the ceramic disk 51 while theramps 55 contact the bosses 13 moves the ceramic disk 51 with thecathode 49 towards or away from the grid aperture 11 depending-upon thedirection of rotation. The spacing from cathode to grid is thus adjustedto a desired distance. The metallic grid cylinder 47 and the metallicretainer ring 53 are then fastened, as by welding, to permanently fixthe cathode 49 with relation to the grid 47 I According to thisinvention, a fully adjustable control of grid to cathode spacing duringassembly is provided. A cathode assembly is provided which is freefloating with respect to the grid aperture. The simplified design andconstruction lends itself readily to automatic assembly, with aresultant saving in manufacturing time and cost. Better operatingefiiciency of the grid-cathode assembly in an electron gun of a cathoderay tube is also provided.

It should be understood that the scope of the invention encompasses theuse of any number of grid end wall bosses for engagement with acorresponding number of ramps for space adjustment. Three ramps andcorresponding bosses, as illustrated, insures proper alignment. Thegradient portions need not be in ramp design, but may take another form,such as studs of varying height. The bosses, described as elongated inthe above examples, may be dimples which are circular or rectilinear.

What is claimed is:

l. A cathode grid assembly for an electron gun including a tubularcathode closed at one end and having an emitting surface on said closedend, a tubular grid having an apertured transverse wall adjacent saidemitting surface, and tubular supporting means insulatingly supportingsaid cathode within said grid, said grid and said tubular supportingmeans having co-operating means on adjacent surfaces thereof forproviding a spiral action relative to each other upon relative rotationfor adjusting the spacing between the emitting surface in said cathodeand said apertured transverse wall.

2. A grid cathode assembly for an electron gun comprising a gridcylinder with an apertured end wall, a cathode having an emitting faceadjacent the aperture in said end wall, and means supporting saidcathode within said grid cylinder, said supporting means having a numberof ramps, said grid end wall having a number of spaced bosses inengagement with said ramps whereby upon relative rotation of saidcathode with respect to said grid cylinder the spacing between saidcathode and said grid dome is adjusted.

3. A grid-cathode assembly for an electron gun com prising a gridcylinder with an apertured end wall, a cathode having an emitting face,and a spacer cylinder supporting said cathode within said grid cylinder,said spacer cylinder having a predetermined number of ramps on onesurface, said grid end wall having a number of spaced projectionscorresponding to said ramps, said spacer cylinder being adapted to berotated with respect to said grid cylinder to provide spacing adjustmentbetween said grid end wall and said cathode emitting face.

4. A grid-cathode assembly for an electron gun com prising a gridcylinder with an apertured end wall, a spacer with an annular end, and acathode assembly, said cathode assembiy being supported by said spacerand insulated from said grid cylinder, said end wall having a number ofbosses therein, said annular end having a number of ramps, said rampsand said bosses being capable of slidable engagement, means to rotatesaid spacer and said cathode assembly with respect to said grid cylinderwhen said ramps and said bosses are engaged thus displacing said spacerand said cathode assembly with respect to said grid end wall, and meansto fasten said spacer in relation to said grid cylinder when a desiredgrid-to-cathode spacing has been effected.

5. A grid-cathode assembly for an electron gun comprising a metallicgrid cylinder, a metallic spacer cylinder which closely fits into said gid Cylinder, a cath q s bly including an emitting face, and a ceramicdisk having a central aperture wherein said cathode assembly ispositioned, means for fastening said ceramic disk and said cathodeassembly within said spacer cylinder, said grid cylinder having a closedend with a number of spaced bosses, said spacer cylinder including aflanged end, having a number of ramps, said ramps engaging said bosses,and slot means for rotating said spacer cylinder within said gridcylinder to adjust the distance between said grid aperture and saidcathode emitting face, and means for fastening said cylinders in fixedrelationship.

6. A grid-cathode assembly for an electron gun including a gridcylinder, a cathode, a ceramic disk and a retainer; said grid cylinderhaving a closed end with an aperture therein, said closed end having anumber of spaced bosses, said ceramic disk having an aperture whereinsaid cathode is fixed, a surface of said disk having a number ofgradient portions, said number of gradient portions corresponding tosaid number of bosses; said disk and said cathode being joined andmovable as an assembly, said assembly being telescoped into said gridcylinder whereby each of said gradient portions engage a correspondingone of said bosses, said assembly being adjustably rotatable withrespect to the grid aperture to vary the distance from the grid apertureto the cathode.

References Cited in the file of this patent UNITED STATES PATENTS2,157,718 Mutscheller May 9, 1939 2,345,642 Varian Apr. 4, 19442,380,946 Cooke Aug. 7, 1945 2,476,060 Moss July 12, 1949 2,481,648 DehnSept. 13, 1949 2,658,393 Woods Nov. 10, 1953 2,717,974 Wihtol Sept. 13,1955 2,808,527 McKenzie Oct. 1, 1957 2,810,851 Johnson Oct. 22, 1957

